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Post by Progenitor A on Oct 29, 2010 9:11:34 GMT 1
Olmy (Oh My!) is too dim to even understand the concept of antenna gain Irony. Didn't you read the link I gave? If you had you would have seen the very obvious first problem with simply adding gains and then interpreting the result in terms of the ratio of input power to output power. If this were valid, it would have to be valid all the way through the system. Look what happens as you add in the various components (in the order of the physical arrangement).... Input power = 1W + 33dB antenna = 2000W + 60dB path loss = 2mW + 33dB antenna = 4W. This obviously breaks down right at the start, with the transmission antenna gain. As the article I linked says antennas do not "magically create power". You can forget the rest of the path - if your 'reasoning' (about gain giving input power to output power ratio) was correct, we have now put 1W in and got 2000W out! All the gains are ratios and you need to understand what they are ratios of.In the transmitter, the antenna gain is "The relative increase in radiation at the maximum point expressed as a value in dB above a standard, in this case the basic antenna..." (taken form the link). What a high gain antenna does is focus it's power in a given direction, rather than just radiating it out in all directions. What all this means is that if I put some 'standard' receiver next to (in the correct direction) our 1W transmitter (fitted with the fancy 33dB antenna), it would receive the same signal as if it were next to a 2000W transmitter that was fitted with a 'standard' (0dB gain) antenna that just spewed all its power out symmetrically. Now, that deals with your original question - your interpretation of the gains as simple ratios of input to output power is just wrong. There is no surprise that adding all the gains in the system and getting a net gain but this does not mean we have got 'something for nothing'. Now, depending on how the references (0dB points) are defined in the rest of the path and how the figure is going to be used, there may well be (probably are) other considerations and some good 'ol engineering 'rules of thumb' that mean that a net loss is more useful than a net gain but I don't know off the top of my head and frankly my interest in this has come to an end...... BTW you made a couple of posts without going out of your way to add some puerile personal insult to me - good to see you are back on form - I was starting to feel neglected  ...  All you have achieved here, Mr Dim, is to repeat the problem I stated in the first case -totally missing the point that we CAN have antenna gains of 33dB and path losseof 60dB, so WHAT is going wrong! You do not even see the problem! Incidentally where on earth do you find your baby-talk 'references'. The article you 'referenced' is one of the dumbest articles I have encountered on radio transmission - you really do have no idea You really are dim! |
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Post by olmy on Oct 29, 2010 9:17:15 GMT 1
All you have achieved here, Mr Dim, is to repeat the problem I stated in the first case! Incidentally where on earth do you find your baby-talk 'references'. The article you 'referenced' is one of the dumbest articles I have encountered on radio transmission - you really do have no idea You really are dim! I will take that as an admission that you are totally flummoxed by my reply and have no answer to it. After all any idiot can say that an argument is 'dumb' and that the person they are talking to is 'dim' - demonstrating it, by actually dealing with the points and pointing out the problems, is another matter....... |
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Post by Progenitor A on Oct 29, 2010 9:28:57 GMT 1
All you have achieved here, Mr Dim, is to repeat the problem I stated in the first case! Incidentally where on earth do you find your baby-talk 'references'. The article you 'referenced' is one of the dumbest articles I have encountered on radio transmission - you really do have no idea You really are dim! I will take that as an admission that you are totally flummoxed by my reply and have no answer to it. After all any idiot can say that an argument is 'dumb' and that the person they are talking to is 'dim' - demonstrating it, by actually dealing with the points and pointing out the problems, is another matter....... Flummoxed indeed! All that is old hat to me You have not even addressed the question that I asked I will ask it again. Why can we in reality get path losses of 60dB and antenna gains of 66db (yes folks, we can actually get a path loss of 60dB and an antenna gain of 33dB)and yet not combine them to get an overall gain? The answer reqyires thought and indicates a real understanding of physics combined with an inquisitive mind and not the blind dismissive reaction that is so commonplace onthis board and has once again been demonstrated here I do not think you even understand the question! Incidentally I insult you in return for the myriad of insults you shower around in your postings - I estimate that 70% of your postings are insulting and that to me, indicates someone whois very dim |
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Post by olmy on Oct 29, 2010 11:27:07 GMT 1
Flummoxed indeed! All that is old hat to me Well, if that is the case, it rather raises the question of why you are not tackling what I have said. After all this is (according to you) your area of expertise - I have never made any claim to be an RF expert. All I have done is take a look at your original 'something for nothing' claim, noted an obvious problem in the first stage, looked up a definition and uncovered a reason why it isn't something for nothing. You seem strangely reluctant to say what is wrong with that.... You have not even addressed the question that I asked I will ask it again. Why can we in reality get path losses of 60dB and antenna gains of 66db (yes folks, we can actually get a path loss of 60dB and an antenna gain of 33dB)and yet not combine them to get an overall gain? No, I haven't answered that question, because what I said (apparently) undermines the reason you gave (in the OP) as to why it is invalid. Prima facie, given what transmission antenna gain means, there is absolutely nothing wrong with adding the gains because, given only that reasonable approximations exist to a 0dB path and a 0dB receiver, then we can see what a total gain of +33dB means and see that it isn't a contradiction. I am perfectly willing to accept that there are reasons why adding the gains in the way you said is not useful for some purpose or other but the trouble is that your own interpretation of what the resulting figure means was wrong - unless you provide a sensible one, your claim is rather meaningless. An additional irony here is that, by your own logic, as applied to other people's explanations of quantum mechanics etc., if I have not understood the question, it is your fault for not explaining it properly........... Incidentally I insult you in return for the myriad of insults you shower around in your postings - I estimate that 70% of your postings are insulting and that to me, indicates someone whois very dim I think you should, perhaps, look at your own posting history. I may well be sarcastic and dismissive in response to specific comments (never to simple, genuine questions) but almost all of my replies include substantive points and the reasons why someone is wrong as well. You go out of your way to insult people (just look at this OP). You start threads the whole point of which is to insult scientists - just look at the titles of some of the threads you have started.... |
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Post by Progenitor A on Oct 29, 2010 11:54:32 GMT 1
Flummoxed indeed! All that is old hat to me Well, if that is the case, it rather raises the question of why you are not tackling what I have said. After all this is (according to you) your area of expertise - I have never made any claim to be an RF expert. All I have done is take a look at your original 'something for nothing' claim, noted an obvious problem in the first stage, looked up a definition and uncovered a reason why it isn't something for nothing. You seem strangely reluctant to say what is wrong with that.... It was stated in my OP that something was wrong. WHY is it wrong is the question you do not seem to grasp If you applied a little thought you may come to realise why it is wrong. Everyone knows you cannot get something for nothing What you CAN (and do ) get is antenna gains of 33dB and path losses of 60 dB WHY can they not be combined in this case is the question No, I haven't answered that question, because what I said (apparently) undermines the reason you gave (in the OP) as to why it is invalid. Good. At least you admit that the question has not been answered Prima facie, given what transmission antenna gain means, there is absolutely nothing wrong with adding the gains because, given only that reasonable approximations exist to a 0dB path and a 0dB receiver, then we can see what a total gain of +33dB means and see that it isn't a contradiction. Prima facie! Engineers do it al the time! I am perfectly willing to accept that there are reasons why adding the gains in the way you said is not useful for some purpose or other but the trouble is that your own interpretation of what the resulting figure means was wrong - unless you provide a sensible one, your claim is rather meaningless. What claim? Engineers up and down th ecountry are doing such additions and subtractions right now An additional irony here is that, by your own logic, as applied to other people's explanations of quantum mechanics etc., if I have not understood the question, it is your fault for not explaining it properly........... I haven't attempted an explanation. I have simply asked a question, repeatedly, in many forms You , by your own admission, have not even attempted to answer that question A question that has not been answered, but which has a quite simple answer based upon physics. All that is required is thought Any good A level student shoule be capable of answering it |
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Post by speakertoanimals on Oct 29, 2010 12:02:38 GMT 1
I think we'd bnest leave him to fester in his own insults on this one - there isn't anything remotely interesting about the supposed problem, apart from a fairly straightforward lesson that equations blindly applied outside their area of application lead to errors, so you'd better understand what lies behind them.
Apart from that, I don't think that this topic is of general enough interest to make it worth defending others against the usual tide of disinformation. Unlike, say, cosmology or quantum theory.
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Post by Progenitor A on Oct 29, 2010 12:12:58 GMT 1
I think we'd bnest leave him to fester in his own insults on this one - there isn't anything remotely interesting about the supposed problem, apart from a fairly straightforward lesson that equations blindly applied outside their area of application lead to errors, so you'd better understand what insights behind them. Apart from that, I don't think that this topic is of general enough interest to make it worth defending others against the usual tide of disinformation. Unlike, say, cosmology or quantum theory. No disinformation here my dear. Nothing to 'defend' Good practical stuff this, based upon physics A straightforward question seeking an answer. Where's Pumblechook I wonder? He would probably know that answer Too difficult for you it seems |
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Post by olmy on Oct 29, 2010 12:18:31 GMT 1
It was stated in my OP that something was wrong. WHY is it wrong is the question you do not seem to grasp If you applied a little thought you may come to realise why it is wrong. Everyone knows you cannot get something for nothing What you CAN (and do ) get is antenna gains of 33dB and path losses of 60 dB WHY can they not be combined in this case is the question The point is that you have just made a claim that adding these things up (when the result is positive) is wrong. The only reason you gave as to why, was that is was "something for nothing" - which it obviously isn't. Perhaps there is a reason in engineering as to why the figure is of more use when it's negative but it clearly means (or can mean) something when it is positive (as my example showed). Remind me again why I should be interested in this detail, which, given your apparent misunderstand of what the total means, may be nothing more than another misunderstanding on your part anyway.... Your continued insistence that engineers do this (something that I have never questioned) rather suggests that you haven't grasped the point I have made. I will try one more time.... I have given one example - a transmission antenna gain of 33dB + 0dB for both the path and the receiver - in which the resulting positive sum has a perfectly valid meaning. You say that this is 'wrong' for some reason. Why? |
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Post by Progenitor A on Oct 29, 2010 13:16:05 GMT 1
It was stated in my OP that something was wrong. WHY is it wrong is the question you do not seem to grasp If you applied a little thought you may come to realise why it is wrong. Everyone knows you cannot get something for nothing What you CAN (and do ) get is antenna gains of 33dB and path losses of 60 dB WHY can they not be combined in this case is the question The point is that you have just made a claim that adding these things up (when the result is positive) is wrong. The only reason you gave as to why, was that is was "something for nothing" - which it obviously isn't. Perhaps there is a reason in engineering as to why the figure is of more use when it's negative but it clearly means (or can mean) something when it is positive (as my example showed). Remind me again why I should be interested in this detail, which, given your apparent misunderstand of what the total means, may be nothing more than another misunderstanding on your part anyway.... Your continued insistence that engineers do this (something that I have never questioned) rather suggests that you haven't grasped the point I have made. I will try one more time.... I have given one example - a transmission antenna gain of 33dB + 0dB for both the path and the receiver - in which the resulting positive sum has a perfectly valid meaning. You say that this is 'wrong' for some reason. Why? It is wrong for the simple reason that it is not absolute power in Watts but equivalent isotropic radiated power in W - EIRP. The power received is never greater than that transmitted quite evidently. But all this is quite irrelevant to the question that I will repeat again. We have real antennas with combined gains of 66dB We have real path losses of 60dB Where does the fallacy of subtracting gains from losses come from? Why is it valid for Path loss> Antenna gain but not the other way around? This is basic physics we are talking about. |
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Post by olmy on Oct 29, 2010 13:38:13 GMT 1
It is wrong for the simple reason that it is not absolute power in Watts but equivalent isotropic radiated power in W - EIRP. The power received is never greater than that transmitted quite evidently. Of course it is - that's what I have been saying. That doesn't make it wrong! It just means that you need to interpret the number correctly. The point is that antenna gain always gives you EIRP. It doesn't suddenly and magically turn into absolute power when the total sum of antenna gains and path loss become negative. But all this is quite irrelevant to the question that I will repeat again. We have real antennas with combined gains of 66dB We have real path losses of 60dB Where does the fallacy of subtracting gains from losses come from? Why is it valid for Path loss> Antenna gain but not the other way around? This is basic physics we are talking about. The thing is that you say it's a fallacy but (as has been shown and you just agreed) it does mean something (it means, in the example I gave, the EIRP). Hence it can only be a fallacy if you interpret it incorrectly. As you haven't said how you are going to interpret it, nobody can possible tell you why it is a fallacy (not based on what you have said anyway). I know there are real antennas and real path losses of the type you keep on about and have never questioned it. Again I suspect you are not grasping the point..... Maybe Speaker is right, this just isn't worth it..... |
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Post by nickrr on Oct 29, 2010 13:41:19 GMT 1
I don't claim to know much about these things but aren't dBs logarithmic? You can't just add them. www.anvtech.com/cgi-bin/db.pl33db + 33dB = 36dB. |
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Post by Progenitor A on Oct 29, 2010 13:52:55 GMT 1
It is wrong for the simple reason that it is not absolute power in Watts but equivalent isotropic radiated power in W - EIRP. The power received is never greater than that transmitted quite evidently. Of course it is - that's what I have been saying. That doesn't make it wrong! It just means that you need to interpret the number correctly. The point is that antenna gain always gives you EIRP. It doesn't suddenly and magically turn into absolute power when the total sum of antenna gains and path loss become negative. But all this is quite irrelevant to the question that I will repeat again. We have real antennas with combined gains of 66dB We have real path losses of 60dB Where does the fallacy of subtracting gains from losses come from? Why is it valid for Path loss> Antenna gain but not the other way around? This is basic physics we are talking about. The thing is that you say it's a fallacy but (as has been shown and you just agreed) it does mean something (it means, in the example I gave, the EIRP). Hence it can only be a fallacy if you interpret it incorrectly. As you haven't said how you are going to interpret it, nobody can possible tell you why it is a fallacy (not based on what you have said anyway). I know there are real antennas and real path losses of the type you keep on about and have never questioned it. Again I suspect you are not grasping the point..... Maybe Speaker is right, this just isn't worth it..... You are totally confusing yourself If we Transmit 1W though a 30dB gain antenna the EIRP is 30dBW If the path losses are 100dB the received power is -70dBW If we put a 30 db Gain antenna at the receiver we receive -40dBW Our received power is 0.1 mW Reducing that path loss to 50dB We transmit 1W through a 30dB antenna EIRP = 30dBW Path loss 50dB then received power = -20dBW If we put a 30 db Gain antenna at the receiver we receive +10dBW Our received power = 10W That is not valid is it now What has gone wrong? This is A level stuff that is easily resolved through a combination of consideration of the nature of the path loss, consideration of the nature of antenna gain and consideration of Maxwells equations for the propagation of electromagnetic waves. Try it , you might learn something. It is not academic it is REAL |
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Post by Progenitor A on Oct 29, 2010 14:01:05 GMT 1
I don't claim to know much about these things but aren't dBs logarithmic? You can't just add them. www.anvtech.com/cgi-bin/db.pl33db + 33dB = 36dB. Yes and yes Yes the dB is logarithmic and yes they are simply added (or subtracted) Here is an example 3 is the logarithm base 10 of 1000: 10 35 is the logarithm base 10 of 100000: 10 5When we add logarithms it is effectively multiplying Thus : 10 3 x 10 5= 10 (3+5) = 10 8So when we add dB we are effectively multiplying and 33dB+33dB= 66db In linear terms 33dB=2000 [dB=10log 10x where x = 2000 in this case] 2000 x 2000 = 4000000 = 66dB PS the link you have given gives the wrong result |
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Post by speakertoanimals on Oct 29, 2010 15:40:30 GMT 1
The linearity assumption for gain at the receiver.
As I said way back, if sunlight is uniform, then double the area, double the power received, whether it is a sunny day or not.
But if instead I have a laser as bright as the sun, then the linearity assumption only holds as long as my receiver is less than the width of the beam. As soon as the beam is narrower than my dish, making the dish bigger gives me no gain in received power.
The meaning of path losses is that in the above, I have taken path losses as meaning the beam same width, just reduced in intensity. but we could also think of it as the beam being widened -- then the differing width of the beam itself alters the cases in which the simple linear gain at the receiver is valid.
With regard to the numbers presented -- just because the supposed power received is less than power transmitted doesn't mean it is the right answer, just possibly not wrong. Whereas when the power received is supposedly more, it is certainly wrong.
As the light example shows, you actually need more information than just these three numbers, in the general case.
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Post by nickrr on Oct 29, 2010 16:26:30 GMT 1
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